Endothelial markers in high altitude induced systemic hypertension (HASH) at moderate high altitude

New strategy for rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments

High-altitude hypoxic environments have critical implications on cardiovascular system function as well as blood pressure regulation. Such environments place patients with hypertension at risk by activating the sympathetic nervous system, which leads to an increase in blood pressure. In addition, the high-altitude hypoxic environment alters the in vivo metabolism and antihypertensive effects of antihypertensive drugs, which changes the activity and expression of drug-metabolizing enzymes and drug transporters. The present study reviewed the pharmacodynamics and pharmacokinetics of antihypertensive drugs and its effects on patients with hypertension in a high-altitude hypoxic environment. It also proposes a new strategy for the rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments. The increase in blood pressure on exposure to a high-altitude hypoxic environment was mainly dependent on increased sympathetic nervous system activity. Blood pressure also increased proportionally to altitude, whilst ambulatory blood pressure increased more than conventional blood pressure, especially at night. High-altitude hypoxia can reduce the activities and expression of drug-metabolizing enzymes, such as CYP1A1, CYP1A2, CYP3A1, and CYP2E1, while increasing those of CYP2D1, CYP2D6, and CYP3A6. Drug transporter changes were related to tissue type, hypoxic degree, and hypoxic exposure time. Furthermore, the effects of high-altitude hypoxia on drug-metabolism enzymes and transporters altered drug pharmacokinetics, causing changes in pharmacodynamic responses. These findings suggest that high-altitude hypoxic environments affect the blood pressure, pharmacokinetics, and pharmacodynamics of antihypertensive drugs. The optimal hypertension treatment plan and safe and effective medication strategy should be formulated considering high-altitude hypoxic environments.

Temporal changes in biomarkers in individuals with and without acute mountain sickness following rapid ascent

BACKGROUND

Field studies have reported conflicting results regarding changes in biomarkers at high altitude. This study measured temporal changes in biomarkers and compared the differences between individuals with and without acute mountain sickness (AMS).

MATERIALS AND METHODS

This study included 34 nonacclimatized healthy participants. Ten-milliliters of blood were collected at four time points: 3 days before ascent (T0), on two successive nights at 3150 m (T1 and T2), and 2 days after descent (T3). Participants were transported by bus from 555 m to 3150 m within 3 hours. AMS was diagnosed using the self-reported Lake Louise Scoring (LLS) questionnaire.

RESULTS

Compared with T0, significant increases in E-selectin and decreases in vascular endothelial growth factor (VEGF) levels were observed at high altitude. Significantly increased C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP-1), and S100 calcium-binding protein B (S100B) levels were observed at T2, and significantly decreased vascular cell adhesion molecule-1 (VCAM-1) levels were observed at T3. Eighteen (53%) participants developed AMS. Changes in E-selectin, CRP, MCP-1, and S100B levels were independent of AMS. Relative to individuals without AMS, those with AMS had significantly higher atrial natriuretic peptide (ANP) and VCAM-1 levels and lower plasminogen activator inhibitor-1 (PAI-1) levels at T1 and higher brain natriuretic peptide and lower VEGF and PAI-1 levels at T3. LLSs were positively correlated with ANP and VCAM-1 levels and negatively correlated with PAI-1 levels measured at T1.

CONCLUSIONS

After acute ascent, individuals with and without AMS exhibited different trends in biomarkers associated with endothelial cell activation and natriuretic peptides.

Epidemiology and pathophysiology of vascular thrombosis in acclimatized lowlanders at high altitude: A prospective longitudinal study

BACKGROUND

Previous literature suggests that thrombosis is more common in lowlanders sojourning at high altitude (HA) compared to near-sea-level. Though the pathophysiology is partly understood, little is known of its epidemiology. To elucidate this, an observational prospective longitudinal study was conducted in healthy soldiers sojourning for months at HA.

METHODS

A total of 960 healthy male subjects were screened in the plains, of which 750 ascended, to altitudes above 15,000ft (4,472m). Clinical examination, haemogram, coagulogram, markers of inflammation and endothelial dysfunction, were studied at three time points during ascent and descent. The diagnosis of thrombosis was confirmed radiologically in all cases where a thrombotic event was suspected clinically. Subjects developing thrombosis at HA were labelled as Index Cases (ICs) and compared to a nested cohort of the healthy subjects (comparison group,(CG)) matched for altitude of stay.

FINDINGS

Twelve and three subjects, developed venous (incidence: 5,926/105 person-years) and arterial (incidence: 1,482/105 person-years) thrombosis at HA, respectively. The ICs had enhanced coagulation (FVIIa: p<0.001; FXa: p<0.001) and decreased levels of natural anticoagulants (thrombomodulin, p=0.016; tissue factor pathway inhibitor [TFPI]: p<0.001) and a trend to dampened fibrinolysis (tissue plasminogen activator tPA; p=0.078) compared to CG. ICs also exhibited statistically significant increase in the levels of endothelial dysfunction and inflammation markers (vascular cell adhesion molecule-1[VCAM-1], intercellular adhesion molecule-1 [ICAM-1], vascular endothelial growth factor receptor 3 [VEGFR-3], P-Selectin, CD40 ligand, soluble C-reactive protein and myeloperoxidase: p<0.001).

INTERPRETATION

The incidence of thrombosis in healthy subjects at HA was higher than that reported in literature at near sea-level. This was associated with inflammation, endothelial dysfunction, a prothrombotic state and dampened fibrinolysis.

FUNDING

Research grants from the Armed Forces Medical Research Committee, Office of the Director General of Armed Forces Medical Services (DGAFMS) & Defence Research and Development Organization (DRDO), Ministry of Defence, India.

Prevalence and Clinical Characteristics of Post-Thrombotic Syndrome in High-Altitude-Induced Deep Vein Thrombosis: Experience of a Single Tertiary Care Center from Real-World Settings

Uday, Yanamandra, Revanth Boddu, Suman Pramanik, Kundan Mishra, Rajan Kapoor, Ankur Ahuja, Tathagata Chatterjee, and Satyaranjan Das. Prevalence and clinical characteristics of post-thrombotic syndrome in high-altitude-induced deep vein thrombosis: experience of a single tertiary care center from real-world settings. High Alt Med Biol. 21:319-326, 2020. Background: Exposure to high altitude (HA) is a recognized predisposing factor for venous thrombosis. Post-thrombotic syndrome (PTS) is a significant late complication, occurring in ∼30%-50% of patients of deep vein thrombosis (DVT). There are not many studies about the characteristics of PTS in patients with HA-DVT. Aim: The aim was to study the epidemiology and clinical characteristics of PTS using a noninvasive Villalta score and identify the risk factors for its development in patients with HA-DVT. Methodology: This is a retrospective single-center observational study (n = 47). The diagnosis of HA-DVT was confirmed using color Doppler ultrasonography at HA. The patients were managed with low molecular weight heparin, followed by vitamin K antagonist therapy till normalization of D-dimer and imaging. The therapeutic target range of >80% was ensured. Villalta scale was used for PTS assessment. JMP 15.0 was used for statistical analysis. Results: All study participants were male with a median age of 34 years, of which 46.81% developed PTS with mean Villalta of 5.29 ± 4.25. The most common symptom was pain (87.23%; n = 41), whereas the most common sign was hyperpigmentation (42.5%; n = 20). On multivariate analysis, the time from onset of DVT and the extent of DVT were related to the development of PTS (degree of freedom [dF] = 5, χ² = 17.34, p = 0.0039) with a likelihood ratio of 4.95 (p = 0.026) and 4.96 (p = 0.026), respectively. The extent of DVT was associated with the severity of PTS (dF = 5, χ² = 12.6, p = 0.0273) with a likelihood ratio of 5.24 (p = 0.022). Conclusions: PTS develops in approximately half of the patients with HA-DVT. The extent of DVT is a significant risk factor for both development of PTS and its severity, whereas time to assessment of PTS from the onset of DVT was associated only with the occurrence of PTS.

Ventilatory parameters at rest after months of stay at 3300 m: A comparison between acclimatized lowlanders and natives at Leh

Background

Increased pulmonary ventilation helps lowlanders and natives to maintain arterial oxygenation at high altitudes. Natives of Ladakh have been shown to have similar ventilatory parameters as Tibetans at 3300 m. But there is limited literature comparing these parameters in Ladakhi natives with acclimatized lowland sojourners.

Methods

End-tidal carbon dioxide partial pressure (EtCO₂), blood oxygen saturation (SpO₂) and hemoglobin concentration (Hb) were measured in 276 participants, 126 native highlanders (NHL - 40 females, 86 males) and 150 acclimatized lowlanders (ALL - 60 females, 90 males).

Results

EtCO₂ was greater in the NHL compared to the ALL, (33.8 ± 3.3 vs 31 ± 2.5 mmHg) although SpO₂ was lower (90.9 ± 2.4 vs 91.7 ± 2.3%). When grouped by sex, NHL males had significantly greater EtCO₂ than NHL females, ALL males and ALL females. Hb and calculated arterial oxygen content was similar in Ladakhis and acclimatized lowlanders, although greater in males compared to females. Systemic blood pressure, heart rate and the proportion of hypertensives was significantly greater in the ALL.

Conclusion

Native Ladakhis, have a significantly greater resting EtCO₂ (especially in males) and lower SpO₂ than acclimatized lowlanders. Blood Hb concentration and oxygen content is, however, similar in natives and acclimatized lowlanders of the same sex.

Vascular Occlusion Restores Endothelium-Dependent Effects of Adenosine Previously Diminished by Diabetes: The Preliminary Report

The aim of this study was to investigate the effect of adenosine in non-occluded or occluded femoral arteries (FA) that were isolated from healthy or diabetic Wistar rats. Determining the role of endothelium, and a transmembrane flow of potassium ions in adenosine actions were also of interest. Diabetes was experimentally induced by alloxan, while the vascular occlusion was performed for 45 min on randomly selected FA. Vascular tone changes were continuously recorded. Selected markers of endothelial dysfunction were measured in animal serum. Thus, adenosine produced a concentration-dependent relaxation of rat FA, which was endothelium-dependent, too, except in a group of diabetic animals. Moreover, serum asymmetric dimethylarginine (ADMA) levels were higher in diabetic animals, thus reflecting endothelial dysfunction (ED). Still, an occlusion of FA enhanced the relaxation effect of adenosine in endothelium-intact rings from diabetic animals. Oppositely, in the presence of high potassium concentration in the buffer, adenosine-induced relaxation was significantly reduced in all of the investigated groups/subgroups. These results suggest that in diabetic animals, an occlusion of FA most probably reversed adenosine-induced relaxation from endothelium-independent into an endothelium-dependent relaxation, thus indicating the possible protective mechanism against ischemic episodes of FA in the presence of diabetes.

Echoes from Gaea, Poseidon, Hephaestus, and Prometheus: environmental risk factors for high blood pressure

High blood pressure (BP) affects over one billion people and is the leading risk factor for global mortality. While many lifestyle and genetic risk factors are well-accepted to increase BP, the role of the external environment is typically overlooked. Mounting evidence now supports that numerous environmental factors can promote an elevation in BP. Broadly speaking these include aspects of the natural environment (e.g., cold temperatures, higher altitude, and winter season), natural disasters (e.g., earthquakes, volcanic eruptions), and man-made exposures (e.g., noise, air pollutants, and toxins/chemicals). This is important for health care providers to recognize as one (or several) of these environmental factors could be playing a clinically meaningful role in elevating BP or disrupting hypertension control among their patients. At the population level, certain environmental exposures may even be contributing to the growing pandemic of hypertension. Here we provide an updated review of the literature linking environment exposures with high BP and outline practical recommendations for clinicians.